This invention concerns a cutting device, particularly for the cutting of predetermined breaking points in plastic membranes, foils or the like, with an air-permeable supporting surface for the plastic membrane or the like, and with an aspirating device, with which the plastic membrane or the like is forced onto the supporting surface.
Plastic membranes or foils are presently utilized in multiple forms. Thus, dashboards of motor vehicles are covered with plastic membranes. Usually airbags for the driver and the passenger next to the driver are integrated into these dashboard panels. Whereas the airbag for the driver is accommodated in the steering wheel, the airbag for the passenger is found behind the dashboard and is covered by an airbag cover. Usually, the airbag cover is covered with a separate plastic membrane and placed over a visible slot in the other part of the dashboard, in order to be able to open simply in the case when the airbag is triggered, and, if necessary, to make possible an exchange of the airbag. Since in the case of a crash, in which the airbag is released, but the entire dashboard need not be replaced, for design reasons, one aims at covering the dashboard with a permeable plastic membrane, by which the airbag is also covered. In order to assure that the airbag can open reliably in the case of a crash, a predetermined breaking point must be formed in the covering membrane, which makes it possible for the airbag cushion to break through the plastic membrane at a specific place.
It has already been attempted to produce this predetermined breaking point by means of a laser by introducing an incision on the back side of the plastic membrane. In the case of laser cutting of the plastic membrane, however, undesired vapors are formed, which must be drawn off. For cutting, the plastic membrane is aspirated or suctioned onto a perforated plate. However, there is the danger that the plastic membrane is applied non-uniformly to the perforated plate, so that the depth of the laser cut varies. If the cut, in which the plastic membrane is only 1 to 1.5 mm thick, however, is too deep, then the predetermined breaking point with time is discernible on the outside of the dashboard, and the desired design effect is destroyed. Also, in the case of such a safety component, a defined residual wall thickness must be assured.
The objective of the invention is thus to avoid the disadvantages that occur in the state of the art and to make possible a more reliable cutting of the plastic membrane.
This objective is essentially resolved with the invention in that the supporting surface is formed by a sintered metal plate. The sintered metal plate has a multiple number of small pores, which make possible a very large aspiration or suction surface with only minimal surface unevenness. In this way, it is assured that the plastic membrane is applied absolutely flatly onto the supporting surface.
According to a preferred embodiment of the invention, the sintered metal plate is built up of several layers, particularly two layers, whereby the upper layer turned toward the plastic membrane or the like, has a finer grain-size distribution than the lower layer. The lower layer of coarser grain size allows for the aspiration of sufficient air, while the upper, small-grained layer assures a uniform distribution of the aspiration effect, and the unevenness of the plastic membrane on the surface of the sintered metal plate is reduced to a minimum.
Appropriately, the sintered metal plate is introduced into a space, which has a vacuum connection. In this way, a uniform suction is assured over the entire surface of the sintered metal plate.
According to the invention, vacuum monitor controls are provided for testing the suction force exerted on the plastic membrane or the like. If an insufficiently strong vacuum is present, then a complete supporting of the plastic membrane on the sintered metal surface cannot be guaranteed and the plastic membrane must be declared as waste.
According to a preferred configuration of the invention, the cutting device has a cutting head with a cutting knife that can be moved over the sintering plate. A purely mechanical cut by the cutting knife is achieved while avoiding the vapors that occur with laser cutting. The blade of the cutting knife is held in a knife holder so that it can be exchanged, so that a simple exchange is possible if there is too great a wear or damage of the blade.
In an improvement of this inventive concept, a measuring device is assigned to the cutting head, by means of which the thickness of the plastic membrane is measured. In this way, a quality control is made possible during the cutting.
Preferably, the measuring device is coupled with a measuring foot, which is spring loaded and is applied onto the plastic membrane or the like during the cutting process. The measuring foot travels along with the cutting knife on the plastic membrane and can thus determine uneven places in the membrane thickness. If these exceed the determined tolerance range, the plastic membrane is worthless. The correct alignment of the sintered metal plate can also be tested by the measuring foot prior to the beginning of the cutting process. For this purpose, the sliding foot is pressed against the sintered metal plastic at several places, in order to recognize a possible inclination of the sintered metal plate. Such an inclination can then be compensated for by means of the CNC control of the cutting device in such a way that the travel path of the cutting knife is adapted to the inclination of the sintered metal plate.
The measuring foot and the cutting knife can be displaced independently of one another according to the invention. Since a uniform residual wall thickness of the plastic membrane will be achieved, the cutting knife must be moved at constant distance, for example 0.5 mm, over the sintered metal plate. The measuring foot, on the other hand, must take into consideration possible unevennesses of the plastic membrane, which can be accomplished due to its spring loading.
In an improvement of the invention, a sliding foot is attached, in a detachable manner, preferably by means of an exchange head, on the side of the measuring foot turned toward the plastic membrane or the like. In this way, a simple exchange of the sliding foot is made possible in case of wear or damage.
In order to minimize the friction resistances during the sliding on the plastic membrane or the like, the sliding foot-has Teflon(trademark) coating or the like, reinforced with fiberglass if needed.
The cutting device according to the invention also has a memory device, in which the data of the membrane thickness measured during the cutting process and/or corresponding theoretical set values can be stored. The memory values can be off-loaded at regular intervals, for example, once a week, into a permanent storage, for example, a writable CD.
Since the quality of the cut in the plastic membrane or the like and thus the safety-relevant properties of the predetermined breaking points essentially depend on the quality of the knife blade, the cutting device, in a particularly preferred form of embodiment of the invention, also has a preferably high-resolution camera, with which the cutting blade can be checked with respect to degree of wear, alignment, breaks or the like. The blade of the cutting knife is checked by the camera and compared with pre-given set values, at regular intervals, for example, before and/or after each cut. A predetermined wear, insofar as it does not exceed an established tolerance range, can be taken into consideration by a corresponding Z-axis correction with the control of the travel path of the cutting blade.
In a further improvement of this inventive concept, a reference blade is assigned to the image section detected by the camera, in which the cutting knife blade is introduced. If the deviation of the blade measurements relative to the reference blade are greater than an established tolerance, then the blade must be exchanged and the last cut plastic membrane or the like must be declared waste.
The cutting device according to the invention also has a bar code printer for introducing a bar code label onto the plastic membrane or the like after cutting. In this way, in the further processing of the plastic membrane, it can be checked whether a cutting process has been conducted and which one.
The cutting device also has an obliterating punch, with which plastic membranes or the like can be marked for waste, if, during their processing, a defect has appeared (insufficient vacuum, overly high deviations in membrane thickness, damage of the cutting knife blade). Then it is checked on subsequent machines whether such an obliterating punch is present and the plastic membrane or the like, as the case may be, is no longer further processed.
In order to increase the processing speed of the cutting device, according to the invention, a multiple number of cutting regions arranged next to one another, particularly four, are provided with sintered metal plates, which can be driven by the cutting head.